Hello everyone....well this is a little embarassing
I have just fitted the space saver spare to my wifes car, first of all let me apologise....the wheel centre measurement is 56.1mm as listed on a variety of websites. When I removed the rear wheels I noticed a very slight gap between what I thought was part of the disc rotor assembly and the actual disc rotor, on further investigation it turned out to be a plastic collar for the aftermarket wheels fitted by the previous owner. Once I removed these the space saver (with the 56.1mm centre) fitted like a glove. One thing I did have to modify was the 3 armed support, which fits to the underside of the boot, as the centre height of the non-genuine space saver was a little high. This meant when I first tried to pull the wheel up the latching groove on the wheel carrier didn't come up high enough to engage with the spring clip, after sanding some plastic off the support arms it eventually fitted...I still don't think it is a very good design though, my wife would struggle to raise/lower the wheel, I guess that's why we have breakdown cover at least she now has a sprare.
Another word of advice for Aussies...don't bother with the Mini dealers, when I contacted the Perth & Sydney offices, the sales staff didn't even realise you could fit a spare and the spares department wanted over $600 AUD, buy it from Mini mania in the US for $354 AUD including freight.
I also fitted a Westfalia towbar, brilliant don't bother with the Hayman Reese bar that all the Australian towbar specialists will try to sell you. The Westfalia doesn't meet ADR, but I think this is because there isn't anywhere for a safety chain to be attached, I got my neightbour to weld a (hardened steel) chain link to the main tube, I have photo's which I will post soon, we will only use the towbar in emergencies if she has to flee from a bushfire and I'm at work with the ute.